1. Law of Dominance: When two contrasting alleles are
present, one (dominant) expresses itself while the other (recessive) remains hidden.
2. Law of Segregation: Alleles separate during gamete
formation. Each gamete receives only one allele for each trait.
3. Law of Independent Assortment: Genes for different traits
are inherited independently of each other.
4. Monohybrid Cross: Tt × Tt → TT : Tt : tt = 1:2:1
(genotypic), 3:1 (phenotypic). Tall : Dwarf = 3:1.
5. Dihybrid Cross: TtRr × TtRr → 9:3:3:1 phenotypic ratio.
Mendel got this ratio with pea plant seed color and shape.
6. In Humans: Female = XX, Male = XY. Sex of child depends
on sperm (X or Y) from father. Mother always gives X.
7. Why is it incorrect to blame mothers? Mother always gives
X chromosome. It is the father's sperm (X or Y) that determines the sex of the child.
8. Homologous Organs: Same origin, different function.
Example: Forelimbs of humans, whales, bats, cats. Indicate common ancestry.
9. Analogous Organs: Different origin, same function.
Example: Wings of birds and insects. Indicate convergent evolution.
10. Vestigial Organs: Reduced, non-functional organs.
Example: Appendix, wisdom teeth in humans. Were functional in ancestors.
11. Fossils: Preserved remains/impressions of ancient
organisms. Show gradual changes over time. Example: Archaeopteryx (link between reptiles and birds).
12. Speciation: Formation of new species when populations
become reproductively isolated due to geographic, genetic, or behavioral barriers.
13. Genetic Drift: Random changes in gene frequency in small
populations. Can lead to loss of certain alleles independent of natural selection.
14. Natural Selection: Organisms with favorable variations
survive and reproduce more. These traits accumulate over generations.
